1. Field of the Invention
The present invention relates to a process for producing a minute-patterned substrate, and more particularly to a process for producing a minute-patterned substrate suitable for use as a grooved substrate for optical disk, a diffraction grating or the like.
2. Description of the Prior Art
There has been known a process for producing a grooved substrate in which a plastic coating film is formed on a substrate from a solution containing a metal-organic compound, then a mold is pressed against the coating film to provide the coating film with a groove pattern corresponding to a ridge shape of the mold, and the coating film is hardened by baking (Japanese Patent Application Laid-Open (KOKAI) Nos. 62-102445 (1987) and 1-119545 (1989)).
The process disclosed in the Japanese Patent Application Laid-Open (KOKAI) No. 62-102445 (1987) has the merit that a grooved substrate for use as an optical disk substrate for information recording can be manufactured comparatively easily. According to this process, however, the setup of the coating film with the mold pressed against the surface of the film is carried out in the atmospheric air and, accordingly, large bubbles may penetrate to the interface between the mold and the coating film, producing hollows in the surface of the coating film. Upon hardening of the film, therefore, the surface of the film may have a large number of hollows. In order to solve this problem, the process disclosed in the Japanese Patent Application Laid-Open (KOKAI) No. 1-119545 (1989) employs a solution containing a thickener in addition to a metal-organic compound as a coating solution, which is applied to a substrate to form a coating film, and a mold is pressed against the coating film under a reduced pressure. Although the latter process prevents large-sized bubbles from being confined between the substrate surface and the mold, minute bubbles on the submicron order may be confined instead. This process therefore has difficulties in producing a substrate which is required to have high surface quality, such as an optical disk substrate. In addition, the process has a disadvantage on an operational basis in that it takes long time to set up the coating film with pressing.